Expansion and contraction characteristics of concrete are well known and it common to utilize contraction and/or contraction-expansion joints at controlled intervals in order to avoid unsightly and even dangerous cracking within the affected areas. When a concrete slab or other aggregrate composition is to be utilized in the vicinity of a swimming pool, it becomes important to control cracking not only from an aesthetic point of view but to thereby prevent water from entering the cracks and penetrating to the soil beneath the slab. Uncontrolled cracking is not only unsightly in a swimming pool environment but any water penetration through to the underlying soil can under expansive soil conditions result in raised and uneven slabs that can even further compound the cracking.
To control such cracking, it is common to utilize either contraction and/or contraction-expansion joints that also accommodate slab expansion.